Television broadcast system



H, -A. WHEELER TELEVISION BROADCAST SYSTEM Jan. 27, 1942.

Filed April 6, 1940 2 Sheets-Shet l willi E ,Tali

INVENTOR H AROLD A. WHEELER ATTORNEY Jan. 27, 1942. H. A. WHEELER TELEVISION BROADCAST SYSTEM Filed April 6, 1940 2 Sheets-Sheet 2 economi ww lNvENToR AROLD A. WHEELER ATTORNEY Patented Jan. 27, 1942 l A s PATENT OFFICE Harold A. Wheeler, Great Nee-k, N. Y., signor to Hazeltine Corporation, a corporation of Delaware Application April 6, 1940, Serial No. 328,351

16 Claims.

Thisvinvention relates to television 'broadcast systems and is particularly concerned with the provision of an improved type of television syn- Cl. P18-6.8)

cnroiiizing signal together with transmitting apthat of the line-synchronizing pulses but less than a line-scanning period, in order to prevent over-lapping any of the line-synchronizing pulses. Such field-synchronizing pulses have components of the line-scanning frequency and 55 a composite synchronizing signal including linethus a television system utilizing such a composlte synchronizing signal is subject to some of the above-mentioned' disadvantages.

. The composite synchronizing signal proposed paratus and receiving apparatus for generating -5 as a standard by the Radio Manufacturers Assoand 4utilizing such signal, respectively.` ciation comprises field-synchronizing informa- In accordance with present television practice, Y tion whichlncludes a modification of the line- '1 there is developed and transmitted a signal synchronizing pulses as Well as the introduction which comprises acarrier wave modulated during of interline broad pulses for field synchronization. successive intervals or trace periods by video "10 The field-synchronizing information is so arsignals and during retrace intervals by the pulses ranged that it Aincludes components in the imof a composite synchronizing signal. At the remediate vicinity of the line-scanning frequency ceiver, it is necessary to provide an arrangement and a system utilizing such a composite synchrofor utilizing certain of the transmitted synchronizing signal .is thus also subject to vsome of the nizing-signal pulses for synchronizing the linel5 above-mentioned disadvantages of other prior scanning operation and for utilizing certain art arrangements.

others of the transmitted synchronizing-signal A preferred type of frequency-responsive pulses for synchronizing the field-scanning opmeans for line-synchronizing pulses in a teleeration. i vision receiver utilizes a resonant circuit sharply In general, it is desirable to supply to each of 20 tuned to the fundamental frequency of the linethe scanning circuits of the receiver only synsynchronizing pulses. Such a selector has the chronizing pulses of the particular type which advantage that the complete obliteration of one are required to synchronize itsV scanning peraor'a few line-synchronizing pulses has little'eifect tion. Intersynchronizing signal-separating aron the synchronization of the receiver, dueto rangements have, therefore, been used for sep- 5 the fact that the free oscillations of the resonant arating the transmitted line-synchronizing and' circuit are effective-to bridge the gap. A preileld-synchronizing pulses. Frequency-responferred type of frequency-responsive means/for sive means have been utilized for effecting the selecting field-synchronizing pulses in a teledesired intersynchronizing. signal separation. vision receiver utilizes a reflecting line, or the However, the composite synchronizing Asignal '30 equivalent, which obliterates substantially all of utilized in prior art systemsv has comprised fieldthe line-synchronizing pulses of the received synchronizing pulses having components of the composite synchronizing signal. Supplementally, line-scanning frequency of the'system and linethere may be utilized with this type of `jfieldsynchronizing pulses having components other synchronizing signal selector a low-pass filter than those of lthe line-scanning frequency of the 35 for reducing the tendency of line-synchronizing system or harmonic -frequencies thereof. Therepulses to cause interference without materially fore, such prior art frequency-responsive interdegrading the edges of the separated field-synsynchronizing signal-separating means have met chronizing pulses. their requirements only. approximately or have In order that the line-synchronizing and fieldbeen of a type, 'such as a differentiating or an 40 synchronizing pulses may be separated from eachv integrating network,lwhich is not the preferred other by arrangements of the above-mentioned type for some television installations. j preferred types, two conditions must be met: For instance, la veryl simple type of prior 'art first, the line-synchronizing pulses must contain composite synchronizing signal comprises very components only of the line-scanning frequency narrow pulses repeated at the line-scanning fre- 45 of the system and at harmonics thereof, and, quency of the system and additional pulses insecond, the field-synchronizing pulses must conseited between certain successive line-synchrotain no components at the line-scanning frenizing pulses at the field-scanning frequency for quency. effecting field synchronization, the additional It is an object of the invention, therefore, to pulses having a Width considerably greater thanl 50 provide an improved television broadcast system which avoids one or more of the above-mentioned disadvantages of such systems of the prior art.

It is a'further object of the invention to provide a television broadcast system which utilizes synchronizing signal suitable for use in a tele-' vision broadcast systemI of the type described.

It is still another object of the invention to provide a television receiving system adapted to receive a composite synchronizing signal utilized in a television broadcast system of the type under consideration.

ing characteristics utilized to explain the operation of the synchronizing-signal selective circuits of the receiver of Fig. 5.

Referring now more particularly to Fig. l of the drawings, there is represented a television transmitting system comprising a signal-generating device I0 of conventional design which may include a cathode-ray signal-generating tube having .the usual electron gun and photosensitive target and line-scanning and field-scanning elements. The system also includes a line-synchronizing pulse generator I2 and a field-synchronizing pulse generator I3 having output circuits connected through line-scanning and fieldscanning generators I2' and I3 to the line-scanning elements and iield-scanning elements, re-

In accordance with the invention, a television broadcast system comprises a station. for developing and transmitting a modulated-carrier wave including means fo'r developing a video `signal, means for developing continuous linesynchronizing pulses, and means for developing a field-synchronizing signal consisting of one or more pairs of field-synchronizing pulses for each field, the pulses of each pair being displaced half the period of the line-synchronizing pulses, effectively having the same area, and having n'o part thereof coincident in duration with the linesynchronizing pulses. Preferably, the pulses of each of the said pairs are similarly shaped.

Means are provided for modulating a carrier wave with the developed signals and pulses and for transmitting the resulting modulated carrier. A station is provided for receiving and reproducing the transmitted carrier wave including means for detecting and reproducing the videofrequency signal. Means are provided in the station, including a circuit sharply-selective to the fundamental frequency of the line-synchronizing pulses, for synchronizing the line scanning of the receiver, means are further provided for synchronizing the field scanning of the receiver, and means are provided forapplying to each of the two last-named means the composite synchronizing-signal component of the received car- -rier signal. Preferably, the means for synchronizing the field scanning of the receiver includes acircuit selectively-responsive to the field-synchronizing signal and having a high attenuation at the fundamental and low harmonic frequencies of the line-synchronizing pulses.

Also in accordance with the invention, a television transmitting system comprises a station for developing and transmitting a modulatedcarrier wave of the type under consideration and, further in accordance with the invention, a television receiving system is provided for receiving and reproducing a modulated-carrier wave of the type under consideration.

For a better understanding of the invention,

together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings, Figs. l and 5 are circuit diagrams, partly schematic, of complete television transmitting and receiving systems, respectively, embodying the present invention; Figs. 2, 3, and 4 are graphs illustrating composite synchronizing signals in accordance with the invention and are utilized to explain the operation of the circuits of Figs. 1 and 5; while Figs. 6, 7, and 8 comprise graphs illustratspectively, of signal generator Ill. In order to provide pedestal impulses for blocking out or for suppressing undesirable impulses in, and ensuring the proper waveform of, the modulation signal developed by the generator I0, there is provided a pedestal-impulse generator I4 having an output circuit coupled to a control element of signal generator I0. In order to synchronize the operations of the generators I2, I3, and I4 and the synchronizing signal-generating apparatus of the transmitter, there is provided a timingimpulse generator I5 effective to generate pulses at the line frequency and pulses at the eld frequency of the system. Generator I5 has .a double-line-scanning-frequency output circuit coupled to generator I2 through a sine-wave generator I6 of double-line-scanning frequency and to generator I3 through generator I6, a frev quency divider I1, and a phase adjustor I8, and also has a line-scanning-frequency output circuit coupled directly to pedestal-impulse generator I4, as presently to be explained.

A video-frequency amplifier 20 is coupled to output circuits of signal generator pedestal generator I4. Connected in cascade to the output circuit of amplifier 20, in the order named, is a frequency changer 2I to which are coupled a local oscillator 22, a carrier-frequency ampliiier 23, a modulator 24, by which the transmitted synchronizing signals are impressed on the generated signal, a power amplifier 25, and an antenna system 26, 21, as shown.

Neglecting for the.-moment the operation of the portions of the system of Fig. l constituting the present invention, the apparatus just described includes the elements of a television transmitting system of conventional design, the individual portions of the system being illustrated schematically since theyv may be of any Well-known suitable construction so that a detailed description of the system and its operation is unnecessary herein. Briefly, however, the image of the scene to be transmitted is focused on the target of the signal generator I0 in whichV generator I0 to suppress or block out the scanning beam during certain portions, particularly the retrace portions, of the scanning cycles and are applied to the video-frequency amplifier 20 to suppress undesirable impulses developed in the system and to aid in obtaining the desired wave form of video-modulation signal.

I2 and light and shade at corresponding incrementalv areas of the image focused thereon, as the beam scans the target, a voltage of correspondingly varying amplitude is developed in the output circuit of the signal generator I and applied to the l amplifier 20. Suitable timing or synchronizing impulses are applied from the generator I to the l'generators I2, I3, and I4 to maintain these generators in synchronism with either the master frequency, in the case of direct camera shots, or the motion picture camera, in case such pictures are being transmitted. The video-signal components applied to the amplifier are amplied therein and thereupon applied tothe frequency changer 2I wherein they are impressed ,upon the carrier wave generated by the oscillator 22. The modulated-carrier signalfis translated jfrom the frequency changer 2I by way of carrier-frequency amplifier 23 to the modulator 24, .wherein the` synchronizing-signal components are impressed on the carrier wave as will be presently explained. The resultant modulated-carrer wave is amplified in the power amplifier 25 and is impressed upon the antenna system 26, 21

Kfor radiation.

Coming now'to the portion of the system in- I volving the present invention, there is provided phase relationship thereto, the generator being -coupled through a phase adjuster 3I to generator I8 which, itself, generates a sinewave of doubleline-scanning frequency. The signal outputs of generators 30 and I3 are combined in a modulator 32 having input circuits coupled. to these generators, while the signal outputs of generators I2 and 32 are combined in mixer-limiter 33 lhaving input circuits coupled to these generators. The output circuit of mixer-limiter 33 is coupled to modulator 24.

Reference is made to Fig. Z for an explanation of the operation ofthe portion of the system of Fig. 1 constituting the present invention. Curve A of Fig. 2 illustrates a portion of the desired composite synchronizing signal of the system for one field in a double-interlaced scanning system, while curve B illustrates a correspending portion of the desired composite synchrpnizing signal for a succeeding field. The narrow pulses L represent line-synchronizing pulses of the system while the broad shaded pulses F represent field-synchronizing signals. The pulses L and F are so proportioned and related, as appears from curves A and B, that the composite synchronizing signal includes a pair of similarly-shaped field-synchronizing pulses for each field displaced half the period of the line-synchronizing pulses of the system and having no part thereof coincident in duration with the line-synchronizing pulses. Furthermore, it will be seen that the line-synchronizing pulses are continuous; that is, the linesynchronizing pulses are not interrupted or modified during the field-synchronizing interval of the system. In the composite synchronizing signais illustrated by curves A and B, the linequency of the system, since the successive pulses F are displaced 180 degrees at the line-scanning frequency and, therefore, have no energy at such frequency. It will be understood that a composite synchronizing signal of this type is developed in mixer-limiter 33 and utilized to modulate the carrier signal in modulator 24 for transmission. Furthermore, it will be understood that, while the pulses F, F have been illustrated as similarly shaped, some of the advantages of the invention will be obtained if they .are not similarly shaped but have effectively the same area.

synchronizing pulses contain components only.

of the line-scanning frequency of the system and harmonics thereof, while the field-synchronizing pulses contain no components at the line fre- In order to develop the line-synchronizingsignais L of the type illustrated, a sine-wave oscillation having a frequency doublel the line-scanning frequency is developed -by generator I6 and utilized to ksynchronize the line-synchronizing pulse generator I 2 which is synchronized at onehalf the frequency of generator I6 and which develops the desired line-synchronizing pulses at line-scanning frequency. In order to insert the pair of field-synchronizing pulses F, F into the composite synchronizing signal, a continuous periodic-pulse wave having a frequency double the lline-scanning frequency and a wave form and pulse duration equal to those of pulses F is generated by generator 30 synchronized by generator I6 through the phase adjuster 3I. The pulses generated by generator 3U have a duration less than one-half the line-scanning period of the system, but long compared to the duration of the line-synchronizing pulses. In order to key desired pulses from the signal output vof puise generator 30 into the circuit of mixer-limiter 33 for insertion into the composite synchronizing signal, the signal output of generator 30 is applied to modulator 32 and a4 keying signal at` field-scanning frequency is also supplied to modulator 32 from the field-synchronizing` pulse generator I3. The keying signal is a periodic-pulse wave at field-scanning frequency, the pulses of which have a 'duration of approximatelyl one line-scanning period and the phase of which is accurately controlled with respect tothe generated line-synchronizing pulsesl by phase adjustor I8 excited from generator. I6 through frequency divider I1.

In summary, therefore, it will be. seen thatk line-synchronizing pulses L, as illustrated in Fig.

modulator 24 to modulate the carrier signal of thesystem. It will be understood that theduration of the pulses F of Fig. 2 is not critical so long as they do not over-lap each other or overlap any of the line-synchronizing'pulses of the system. The television broadcast system, therefore, comprises the station for developing and transmitting a modulated-carrier Wave including, a signal generator I0 for developing a video signal, line-synchronizing pulse generator I2 for developing continuous line-synchronizing pulses,

units I3, 30, and 32 for developing a field-synchronizing signal consisting of one or more pairs of pulses for each field displaced half the period of the line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with the line-synchronizing pulses, and modulator 24 for modulating a carrier wave with the developed signals and pulses for transmission.

While the transmitter of Fig. 1 has been described as generating a composite synchronizing signal as illustrated by curves A and B of Fig. 2,

it will be understood that, with proper control nizing pulses, although they do not over-lap such pulses:

In other words, the composite synchronizing signal illustrated by any of Figs. 2, 3, and 4 comprises continuous line-synchronizing pulses and a field-synchronizing signal consisting of a pair of similarly-shaped field-synchronizing pulses for each field displaced half the period of the line-synchronizing pulses and having no part thereof coincident in duration with the line-synchronizing pulses. Also, in each case, the pair of field-synchronizing pulses for.one eld is effectively included between two successive line-synchronizing pulses and the pair of field-synchronizing pulses for the succeeding eld is separated by the duration of aline-synchronizing pulse. Further, if desired; more than one pair of field-synchronizing pulses F, F per field mayV be utilized, it only being necessary that the number of such pulses be even and that each pair be displaced by one-half the line-scanning period so that the resultant signal contains no energy at the line-scanning frequency.

Referring now to Fig. 5, the system there represented comprises a television receiver of the superheterodyne type for receiving and reproducing a television signal in accordance with the present invention. This receiver includes an antenna system 40, 4l to which there are connected in cascade, in the order named, a radio-frequency amplifier 42, a frequency changer or osquency signal is also applied from the amplifierv 46 through synchronizing-signal separator 5I to the apparatus 50 wherein automatic amplification control or A. V. C. potentials are developed in accordance with the present invention and applied to the control electrodes of one or more of the tubes of units 42, 43, and 44 and wherein the line-synchronizing and field-synchronizing components are effectively separated from each other and applied to the scanning circuits 48 and 49, as will be hereinafter further explained. Sawtooth current or voltage scanning waves are developed by the line-scanning and field-scanning circuits 48 and 49 and applied to the scanning l is provided in unit means forv effectively sepacillator-modulator 43, an intermediate-frequency amplifier 44,'a detector 45, a video-frequency amplifier 46, and an image-reproducing device 41. A line-scanning circuit; 48 and a field-scanning circuit 49 are also coupled to the output circuit of video-frequency amplifier 46 by way of a synchronizing-signal selector 5i and intersynchrcnizing signal-separating apparatus 50 embodying the present invention and hereinafter described in detail. The circuits 48 and 49 are coupled to the scanning elements of the imagereproducing device 41 in a conventional manner. The circuits. or elements 4@--48, inclusive, and tl may all be of any conventionalwell-known construction, so that detailed illustrations and descriptions thereof are unnecessary herein.

Referring brieily to the general operation of the receiving system, television signals are selected by the antenna system 48, 4t, amplified in the radio-frequency amplifier 42, and converted into intermediate-frequency signals in the oscillator-modulator d3, the intermediate-frequency signals being, in tum, selectively ampliied in the intermediate-frequency amplifier 44 and delivered to the vdetector 45. The videomodulation components of the signal are developed by the detector 45 and are supplied to the iii) l separated field-frequency pulses.

rating the transmitted field-synchronizing pulses from all other components, means for effectively separating the transmitted line-synchronizing pulses' from all other components, and means for developing an A. V. C. bias for controlling the amplification of the received signal inversely in accordance with the received amplitude there of. As stated above, the preferred type of frequency selection for the line-synchronizing pulses is a resonant circuit sharply-tuned to the linescanning frequency. This has the advantagel that the complete obliteration of one or a few line-synchronizing pulses has little effect on the synchronizing of the scanning circuits, the free oscillation of the resonant circuit bridging the' gap. Accordingly, there is provided in unit 50 a selector 52 including a single sharply-tuned or low power factor parallel-resonant circuit 53, 54. 'I 'he line-scanning circuit 48 is coupled to the selector 52 through a phase shifter55 and a pulse shaper 5S.

Also, as stated above, the preferred selectionk of field-synchronizing pulses is by the use of a reflecting line or equivalent network which obliterates substantially all of the line-synchronizing pulses and leaves the field-synchronizing pulses substantially undegraded and with fairly steep edges. Such a network may be supplemented by a low-'pass filter to reduce the tendency for interference from the line-synchronizing pulses without materially degrading the edges of the Accordingly, there is coupled to synchronizingesignal selector 5l a unit 58 which includes the elements ofa.

Y the frequency of the line-synchronizing pulses,

condenser 13 is also coupled in parallel with these resonant circuits. Field-scanning circuit 49 is coupled to unit 59 through a rectifier 60.

An A. V. C. rectifier 15, which may be of conventional design, but which preferably includes a load circuit having a time constant which is short relative to the period of the field-synchronizing pulses to provide a fast-acting automatic amplification control system, is coupled across tuned circuit 53, 54 and has its output applied to one or more of the tubes in the stages 42, 43, and 44 in order toA maintain the signal input to detector 45 Within a relatively narrow range for a Wide range of received signal intensities.

Coming now to an explanation of the portion 50 of the receiver which constitutes the essence of the present invention, it is seen that synchronizing-signal selector comprises means for applying to the unit 50 the composite synchronizing-signal component of a received carrier sig- -L nal and reference Yis made to Fig. 6 wherein are shown certain of the response characteristics of the receiver circuit. Solid-line curve C illustrates the response characteristic of the unit 59, which is the substantial equivalent of a reecting filter, as supplemented by the action of the unit 58. The characteristic of the low-pass filter of unit 58 alone is illustrated by dashed-line curve D,

while the sharply-selective response characteristic of tuned circuit 53, 54, which is resonant at is illustrated by the dotted-line curve E. The frequency scale of the graph of Fig. 6 is divided into multiples of the line-scanning frequency f1. It is noted that the reflecting filter, having the characteristic C, effectively suppresses or infinitely attenuates components of frequencies equal to all multiples of the line-scanning frequency; that is, the circuit provides a high attenuation at the fundamental and predetermined harmonic frequencies of the line-synchronizing pulses. 'Ihis action is procured in the circuit of Fig. 5 by proportioning circuit 61, 68 to be reso-` nant at the frequency fr, proportioning circuit 69, 10 to be resonant at the frequency fz, proportioning circuit 1l, 'I2 to be resonantat the frequency f3, while a trap at the frequency f4 is effectively provided by the tuned circuit 83, 64

included in the series arm of low-pass filter netwprk 58. This circuit arrangement is then effective to provide a high attenuation at zero freqlency, the fundamental frequency, the second Harmonic and the third harmonic frequencies of the line-synchronizing pulses and, obviously, the pass band of the filter network 58 may be widened and a correspondingly greater number of series-resonant traps may be included in the network 59 if it is desired to increase the fidelity of translation of the field-synchronizing pulses.

In Fig. 7, there is illustrated the signal output of unit 59 in response to an input composite synchronizing signal of curve Aof Fig. 2, the linesynchronizing pulses being effectively suppressed or infinitely attenuated. While the system produces inverted images of the field-synchronizing pulses, these occur at such a time that they do not interfere with the field-synchronizing operation of the receiver.

In Fig. 8, there are illustrated some of the outh put characteristics of the line-synchronizing pulse selector 52 of the receiver of Fig. 5. The solidline curve F represents the sine-wave voltage developed across the resonant circuit 53, 54 while the dotted-line curve G represents the voltage which is developed at the output circuit of phase shifter 55. The phase shifter 55. is effective to provide a sine-wave output which is Ashifted. in phase with respect to thevoltage of curve F so that its zero-axis intercepts coincide with the leading edge of the line-synchronizing pulses L. The dotted lines H of Fig. 8 illustrate a series ofA sharp'pulses which are derived from the displaced sine Wave G and which are exactly timed with the leading edge of the line-synchronizing pulses L. The pulse shaper 56 for deriving such narrow pulses H from the sine-wave output G of phase shifter 55 may be of conventional design. In fact, the phase shifter 55, pulse Shaper 56, and the line-scanning circuit 48 may Vcomprise elements in accordance with those shown in U. S. Patent No. 2,251,929, issued Aug. 12, 1941, to Freeman and Blaisdell. Specifically, phase shifter 55 may comprise a tuned circuit inductively coupled to tuned circuit 53, 54 thus corresponding to the tuned circuit 25, 2B of .the above-mentioned United States patent. Pulse shaper 56 may comprise a diode rectifier, corresponding to the diode rectifier 50 of the said-United States patent, coupled in series with an inductance across the phase shifter 55V to which is coupled a. multigrid output tube, corresponding to the tube 5l) of the said United States patent, for supplying the developed line-synchronizing pulses to the line-scanning circuit 48 for synchronizing a scanning oscillator therein. Since none of the comquency, the line-synchronizing pulses .derived from the selector 52 are unaffected by such fieldsynchronzing components. At the same time, these output pulses are substantially free from transient disturbances and noise and will persist even though one or more of the line-synchronizing input pulses may be obliterated, due to the iiy-wheel or energy-storage properties of the resonant circuit 53, 54.

The line-synchronizing signal input to the A. V. C. rectifier 15 is of such a nature as to permit the use of a short time-constant load circuitv in the A. V. C. rectifier circuit, thereby to provide a fast-actingv A. V. C., which is of decided advantage in avoiding the paralyzing effects of large amplitude noise disturbances on long timeconstant A. V. C. circuits. This advantage is incidental to the use of the method provided for selecting Vthe line-synchronizing pulses without disturbance from the field-synchronizing pulses. since, otherwise, the time constant of the A. V. C. rectifier load circuit must be sufficiently large to filterout such field-scanning frequency components. The type of synchronizing signal provided by the invention thus mairesI possible the utilization of this type of fast-acting automatic amplification control circuit with its full advantages.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A television broadcast system comprising, a station for developing and transmitting a modu lated-carrier wave including means for developg ing a video signal, means for developing continuous line-synchronizing pulses. means for developing a eld-synchronizing signal consisting of one or more pairs of pulses for each iield displaced half the period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses, means for modulating a carrier wave with said developed signals and pulses for transmission, a station for receiving and reproducing said carrier wave including means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizingthe line scanning of said receiver, means for synchronizing the eld scanning of said receiver. and means for applying to each of said two lastnamed means the composite synchronizing-signal component of a received carrier signal.

2. A television broadcast system comprising, a station for developing and transmitting a modulated-carrier wave including' means for developing a video signal, means for developing continuous line-synchronizing pulses, means for developing a field-synchronizing signal consisting of one or more pairs of pulses for each field displaced half the period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses, means for modulating a carrier wave with said developed signals and. pulses for transmission, a station for receiving and reproducing said carrier wave including means for detecting and reproducing said video signal, means including a. circuit sharplyselective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means including a circuit selectively-responsive to said eld-synchronizing signal and having a high attenuation at the fundamental and predetermined low harmonic frequencies of said line-synchronizing pulses for synchronizing the field scanning of said receiver, and means for applying to each of said two last-named means the composite synchronizing-signal component of a received carrier signal.

3. A television broadcast system comprising, a station for developing and transmitting a modulated-carrier wave including means for developing a video signal, means for developing continuous line-synchronizing pulses, means for developing a field-synchronizing signal consisting of one or more pairs of similarly-shaped field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and having no part thereof coincident in duration with said line-synchronizing pulses, means for modulating a carrier wave with said developed signals and pulses for transmission, a station for receiving and reproducing said carrier wave including means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said linesynchronizing pulses for synchronizing the line scanning of said receiver, means for synchronizing the iield scanning of said receiver, and means for applying to each of said two last-named means the composite synchronizing-signal component of a received carrier signal.

4. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous line-synchronizing pulses and a held-synchronizing signal consisting of one or more pairs of field-synchronizing pulses for each eld displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective tothe fundamental frequency of s'aid line-synchronizing pulses for synchronizing the line scanning of said receiver, means for synchronizing the field scanning of said receiver, and means for applying to each of said two lastnamed means the composite synchronizing-signal component 0f a received carrier signal.

5. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous line-synchronizing pulses and a fieldsynchronizing signal consisting of one or more pairs of held-synchronizing pulses for each iield displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means including a circuit selectively-responsive to said field-synchronizing signal and having a high attenuation at the fundamental and predetermined low harmonic frequencies of said line-synchronizing pulses for synchronizing the field scanning of said receiver, and means for applying to each of said two last-named means the composite synchronizing-signal component of a received carrier signal.

6. A television receivingsystem for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous line-synchronizing pulses, and a field-synchronizing signal consisting of one or more pairs of similarly-shaped field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means for synchronizing the field scanning of said receiver, and means for applying to each of said two last-named meansV the composite synchronizing-signal component of a received carrier signal.

7. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous liner-synchronizing pulses and a fieldsynchronizing signal consisting of one or more pairs of field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof 'coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said vdeo signal, means including a low power l factor parallel-resonant circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means for'synchronizing the field scanning of said receiver, and means for applying to each of said.two last-named means the composite synchronizing-,signal component of a received carrier signal.

8. A television receiving system for receiving and reproducing a modulated-carrier wave including'as modulation components a video sig- `nal, continuous line-synchronizing pulses and a field-synchronizing signal consisting of one or more pairs of field pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means effectively including in cascade a low-pass filter and a circuit selectively responsive to said field-synchronizing signal and having high attenuation at the fundamental and predetermined low harmonic frequencies of said line-synchronizing pulses for synchronizing the field scanning of said receiver, and means for applying to each of said two last-named means the composite synchronizing-signal component of a received carrier signal.

9. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video, signal, continuous line-synchronizing pulses and a l field-synchronizing signal consisting of one or more pairs of field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the linevscanning of said receiver. Ine-ans in-r cluding a circuit selectively responsive to said field-synchronizing signal and having a high attenuation at zero frequency, the fundamental frequency, the second harmonic and the third harmonic frequencies of said line-synchronizing pulses for synchronizing the field scanning of said receiver, and means for applying to each of said two last-named means the composite synd chronizing-signal component of a received carrier signal.

10. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous line-synchronizing pulses and a field-synchronizing signal consisting of one or more pairs of field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing s'aid video signal, means including a, circuit sharply-selective to the fundamental fre'guency of said line-synchronizing pulses for synchronizing the. line scanning of said receiver, means for synchronizing'the field scanning of said receiver, means for applying Ito each ofsaid two .lastnamed lmeans .the lcomposite -synchronizing-signal component of a received-carrier signal, and means including a fast-.acting automatic amplification'control-rectifier circuit responsive to/ the output of said sharply-selective circuit for controlling the amplification of said receiver inversely in accordance with received signal intensities.

11. A television receiving system for receiving and reproducing a modulated-carrier wave including as modulation components a video signal, continuous line-synchronizing pulses and a field-synchronizing signal consisting of one r more pairs of similarly-shaped field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses comprising, means for detecting and reproducing said video signal, means including a circuit sharply-selective to the fundamental frequency of said line-synchronizing pulses for synchronizing the line scanning of said receiver, means for synchronizing the field scanning of said receiver, means for applying t0 each of said two last-named means the composite synchronizing-signal component of a received carrier signal, and rectifier means responsive to the signal 'output of said sharply-selective circuit and provided with a load circuit having a time constant which is short relative to the period of said fieldsynchronizing pulses for controlling the amplificatiyon of said receiver inversely in accordance with received signal intensities.

12. A television transmitting system compris'- ing, a station for developing and transmitting a modulated-carrier wave including means for developing a video signal, means for developing continuous line-synchronizing pulses, means for developing a field-synchronizing signal consisting of one or more pairs of field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses, and means for modulating a carrier wave with said developed signals and pulses for transmission.

13. A television transmitting system comprising, a station for developing and transmitting a modulated-carrier wave including means for developing a video signal, means for developing continuous line-synchronizing pulses, means for developing a field-synchronizing signal consisting of one or more pairs of similarly-shaped field-synchronizing pulses for each field displaced half a period of said line-synchronizing pulses and having no part thereof coincident in duration with said line-synchronizing pulses, and means for modulating a carrier wave with said developed signals and pulses for transmission.`

14. 'A television transmitting system comprising, a station for developing and transmitting a.

modulated-carrier wave including means for developing a vvideo signal, means for developing continuous line-synchronizing pulses, means for developing a field-synchronizing signal consist-- ing of apair of field-synchronizing pulses for each field displaced half a period of the linesynchronizing pulses and effectively having the same area and having no part thereof coincident in duration with said line-synchronizing pulses, said field-synchronizing pulses having a duration less than one-half the line-scanning period of said system but long compared to the duration velopng a video signal, means for dvelppin continuous line-synchronizing pulss,mansf developing va periodicfwlse-ffwave navngfaifr l s quency twice that` vof, ,asad -.linesynch19112lng pulses, means Afor selectngprevdetermined- Qnes ing a e1dsynchronizng,signa .co u d or more' pairs vof similarly-shaped; eldv-s nizing pulses .for each-egdfd sp1acedhal1f;af p` riod of said-line-synchronizingpulss Aand hay no -panrtv thereof coincdentfinduratiomWlfh line-s'ynchvonizing pulses, and; mgans Vf o`r mod1f1` lating Tariarrierfwayawthssad d andpulses for 'transmission 16. A televisioni,transmigtingsysmomprf Y ing, a stationnfor developingzandtransmttng 'a modulated-carrier, wavefincluiingj mear'xsl fr" e- 

